Remember that a sleeping bag is a PASSIVE heating device. It does not make heat, it juts traps what your body makes.
Akichows advice sounds very much like what I do. I agree a 32 bag is not likely warm enough, but much depends on age, metabolism, experience, wind, fatigue, altitude, ground temp, etc, etc.
Some other tricks of the trade:
Do not go to bed damp. Always change into dry socks and dry t-shirt before adding my top fleece and/or bottom silk or wool long johns, when needed.
Don't wait until it is dark and you are tired and your metabolism is shutting down. Get in your bag sooner rather than later.
If you have been hanging around camp and cooling down, walk up and down the trail for 10-15 minutes and warm back up (but not enough to sweat) and then get in your bag.
Before bed, throw in a couple of those chemical hand/foot warmer packets and pre-warm your bag. You would be surprised how much this little bit helps. I have had to throw them out.
For really, really cold places....before bed, heat on your stove to near-boiling one (or two) Nalgen bottles of water, cap them tightly, place them in your bag. Serious stuff. (Don't worry, the Nalgen can take it.) Also, you can wrap the hot water bottles in a stuff sack to prevent too-hot surface touching your body. Also, this hot water bottle thing is a good way to keep warm batteries and liquids like lotion, eye drops, saline nasal spray, etc, etc.
Everyone knows to wear hats, balaclava, long sleeves, dry socks, etc in the bag. But wearing gloves is often not done, but is amazingly helpful.
